Siew-Win started her career with the Ministry of Education as an early pioneer with the Psychological Services Division in the mid-80s. She played a key role in leading the setup of the Learning Support (Special needs) Programme at numerous schools.

After a number of years, Siew-win branched out into private practice where she setup and successfully ran Poon & Associates for 10 years. During that time, she was personally involved in managing a multi-disciplinary team to provide Occupational, Educational, Art and Speech therapy services. She also developed a more diverse client base from local and international schools in Singapore and around the region.

Following her move to Shanghai as a trailing spouse, she worked within a mental health team in a well-established chain of medical clinics, dealing mainly with the expatriate population.

Beyond her private practice, Siew-Win served as Clinic Director and supervised postgraduate students at James Cook University Singapore. She is also supervisor to students from the Applied Psychology Masters programme at the National Institute of Education, Nanyang Technological University. In addition, she had taught the special needs component for the Diploma in Early Childhood Education at the Kinderland Academy.

Siew-Win has contributed to numerous magazine articles, radio and TV programmes about child development and special needs. She was trained at University College London where she obtained her Masters in Educational Psychology and is a Chartered Psychologist with the British Psychological Society and a Registered Psychologist with the Singapore Psychological Society.